The successful outcome of RSA depends greatly on proper soft tissue tension in the shoulder joint. The stability of the shoulder joint is generally maintained from significant deltoid tension holding this ball and socket joint together. Some RSA systems require the surgeon to use a trial and error approach in establishing proper soft tissue tension. Such approaches often take several attempts before adequate stability is achieved.
When performing a trialing step in a reverse shoulder procedure, one important aspect is to determine the correct height of the humeral insert implant that will ultimately be chosen for the patient. A series of humeral insert trials with varying heights is normally utilized to determine the correct height for the implant. By using thicker or thinner insert trials the soft tissue tension and joint range of motion can be optimized for the patient.
Such trialing procedures generally include selecting a first trial insert, installing it into other parts of the shoulder system, reducing the joint, and then checking the joint for soft tissue tension and range of motion. The joint is then dislocated, and if the correct humeral insert implant height has been determined the reverse shoulder implantation proceeds. When the correct trial is determined, the soft tissue tension is significant, requiring the surgeon to apply extreme force to the humerus and surrounding soft tissues to reduce the joint. If no additional damage is done during this reduction process, the joint must then be dislocated to allow the surgeon to implant a joint replacement prosthesis.
If the correct humeral insert height has not yet been determined, then a second trial insert with a different thickness than the first trial is selected. The second trial insert is installed and the joint is assessed. As a result of the trialing procedure, the reverse shoulder joint can be reduced and dislocated multiple times.
Traditionally, each time the reverse shoulder joint is reduced and dislocated, the soft tissue has to be stretched in order for the glenosphere to be placed in or removed from the humeral insert. This stretching of the soft tissue can lead to joint instability and increased recovery time for the patient.